Conventionally, to supply hydrogen used as fuel of a fuel-cell-powered vehicle or to store liquefied oxygen under a severe use condition such as a cosmic space, a high-pressure tank which enhances the pressure tightness is used.
Particularly, Japanese Patent Laid-Open 2002-188794 describes the high-pressure tank in which a tank base body is constituted of a liner made of high-density polyethylene and reinforcement fibers such as carbon fibers to which an adhesive agent such as epoxy resin is applied and which are wound around an outer surface of the liner.
In such a high-pressure tank, the reinforcement fibers are wound around the outer surface of the liner while applying a fixed winding tension to the reinforcement fibers and, after finishing the winding operation, the epoxy resin which is applied to the reinforcement fibers or the like is hardened by hardening treatment under given conditions thus forming a pressure shell.
Further, after hardening the epoxy resin, in a state that the inside of the high-pressure tank is emptied, no stress is applied to the pressure shell.
In such a high-pressure tank, when the pressure inside the high-pressure tank is elevated along with the filling of gas or liquid to the inside of the high-pressure tank, as shown in FIG. 11, to the reinforcement fibers of an inner-side portion of the pressure shell, a tensile stress which is larger than a tensile stress applied to the reinforcement fibers of an outer-side portion of the pressure shell is applied and hence, a limit pressure of the high-pressure tank is determined when the stress which is applied to the reinforcement fibers of the inner-side portion of the pressure shell exceeds a tension limit of the reinforcement fibers.
In this case, in spite of the fact that the reinforcement fibers of the outer-side portion of the pressure shell do not reach the tension limit, the limit pressure of the high-pressure tank is determined and hence, a value of the limit pressure is relatively small.
Accordingly, a range of application of a product provided with the pressure shell is narrowed thus giving rise to a drawback that the availability of the pressure shell is lowered. Particularly, when the high-pressure tank provided with such a pressure shell accommodates gas therein, a gas accommodating quantity is decreased due to the small limit pressure.
Accordingly, inventors of the present invention have tried to increase the value of the limit pressure by lifting the pressure value inside the high-pressure tank at which the reinforcement fibers of the inner-side portion of the pressure shell reaches the tension limit to the pressure value inside the high-pressure tank at which the reinforcement fibers of the outer-side portion of the pressure shell reaches the tension limit, and have made studies and developments, and have arrived at present invention.